Pendulum for gravity determination



Jan. 15, 1935.

O. MEISSER PENDULUM FOR GRAVITY DETERMINATION Filed March 8, 1952 In Yen/qr:

Que

Patented Jan. 15, 1935 PATENT OFFICE 1,987,786 PENDULUM FOR GRAVITY DETERMINATION Otto Meisser, Jena, Germany, assignor to the firm of Carl Zeiss, Jena, Germany Application March a, 1932, Serial No. 597,526

In Germany March 14, 1931 6 Claims.

I have filed an application in Germany, March With a view to give the decisive values of a pendulum for gravity determination the desired magnitudes, the ready made pendulum has been carefully treated until the required result is obtained as far as possible. In addition to other disadvantages, this method is far from being practical in so far as the mass of the pendulum, when erroneously diminished beyond the required measure, may not be increased. According to the present invention the pendulum is provided with adjusting screws, and these adjusting screws are given such positions that their axes lie in a plane containing the knife edge of the pendulum. The desired adjustment is arrived at by giving the screws suitable lengths, that is to say correct masses. To this effect, screws are applied which have lengths slightly superior to those required. When provided with these screws, the pendulum is carefully tested, and the screws are filed until they are exactly reduced to the masses they are to have. If the axes of the screws lie in a plane containing the knife edge of the pendulum, an eventual loosening of the screws cannot influence the time of swing of the pendulum. However, this influence is avoided completely only when, in adclition to lying in the said plane, the axes of the screws are parallel to the knife edge. The pendulum is preferably constructed as a so-called minimum pendulum, that is to say as a pendulum the centre of gravity of which is at a distance from the knife edge which is equal to half the length of a simple pendulum having the same time of swing. The time of swing of a pendulum of this kind is comparatively indifferent to slight displacements of the knife edge.

Providing adjusting screws permits to so arrange these screws that the decisive values of the pendulum can be adjusted independently, or at least practically independently, of each other. In a minimum pendulum, a screw the axis of which passes approximately through the centre of gravity of the pendulum influences for instance only the time of swing of the pendulum. A screw the axis of which passes through the centre of oscillation of .the pendulum influences only the relation existing between the distance of the centre of gravity from the knife edge and the reduced length of pendulum, and it therefore permits to adjust the pendulum in such a manner that this pendulum becomes a minimum pendulum. Finally, a pair of adjusting screws the axes of which pass approximately through the knife edge suspension and the centre of oscillation, re-

spectively, permit to adjust the mass of the pendulum without influencing the aforesaid adjustments.

It is convenient to provide the body of the pendulum with a temperature compensating body the coefficient of expansion of which is greater than that of the body of the pendulum, and to fix to the pendulum that part of this temperature compensating body which is farthest from the centre of gravity of the pendulum. If, for instance, a rise of temperature causes the body of the pendulum to expand, the center of gravity of this body will wander downwardly; reversely, an increasing temperature makes the center of gravity' of the compensating body go upwardly, the consequence being that by means of this compensating body the influence of the temperature on the time of swing of the pendulum is at least greatly reduced. When rectifying the determinations of oscillation, the temperatureneed be determined with less exactitude, which is of special importance when the pendulum is to be used in the open. By providing the compensating body in the interior of the pendulum body it is possible to give the pendulum a simple and compact form. 2

In this case disturbing variations in the length of the pendulum are to be feared to a very slight extent only, and eventually adhering impurities can be easily removed.

As results from the underlying relations, the temperature influence eventually still obtaining is smallest when the compensating body approximately reaches the centre of gravity of the pendulum.

The upper end of the body of the pendulum having to be traversed by the knife edge, it is convenient to fix to the pendulum that end of the compensating body which is farthest from the centre of gravity of the pendulum.

The accompanying drawing represents an example of the invention in a longitudinal section.

The body of the pendulum consists of a cylindrical bar a of invar steel which is provided near its upper end with a knife-edge body I). The lower half of the bar a has a cylindrical bore 0. This bore is closed below by means of a threaded bolt d of invar steel the upper end of which is soldered to a brass cylinder e serving as a compensating body. The compensating body extendr is a minimum pendulum. Closely below the knifer edge body b, the bar a has a screw f the axis of which is parallel to the axis of the knife edge.

At the centre of gravity of the pendulum another screw being parallel to the knife edge.

screw 9 is screwed into the bar a,the axis of this At the centre of oscillation of the pendulum two screws h and i are provided at either side of the pendulum, and the axes of these screws are also parallel to the knife edge. The object of the screw g is to adjust the time of swing, that of the screws h or i to so adjust the pendulum as to make it a minimum pendulum. The screws and i (or provided that i is used for the just mentioned adjustment, f and h) serve for adjusting the mass of the pendulum.

I claim:

l. A pendulum for gravity determination, comprising a pendulum body, a knife edge attached prising a pendulum body, a knife edge attached to the pendulum body, the centre of gravity of to the pendulum body, and an adjusting screw being provided in the pendulum body, the axis of this adjusting screw passing approximately through the centre of oscillation of the pendulum,

4. A pendulum for gravity determination, comprising a pendulum body, a knife edge attached to the pendulum body, and a pair of adjusting screws, one of these adjusting screws being provided in the pendulum body near the knife edge, and the axis of the other of these adjusting screws passing approximately through the centre of oscillationof the pendulum.

5. In a pendulum for gravity determination according to claim 1 having a hollow portion, a temperature compensating body, the coefiicient of expansion of this body being greater than that of the pendulum body, the temperature compensating body being inserted into the said hollow portion, and that end of this temperature compensating body which is farthest from the centre of gravity of the pendulum being fixed to the pendulum body.

6. In a pendulum for gravity determination according to claim 1 having a hollow portion, a temperature compensating body inserted into the said hollow portion, the coeflicient of expansion of this body'being greater than that of the pendulum body, the lower end of this temperature compensating body being fixed tothe lower end of the pendulum body, and the upper end of the temperature compensating body reaching approximately the centre of gravity of the pendulum.

O'II'O MEISSER. 

